Disruption of giant molecular clouds by massive star clusters

by Canadian Astronomical Society

(PhysOrg.com) -- New computer simulations show that the light from massive stars is, by itself, enough to blow apart the nebula where the stars are born. While this 'radiation pressure' was by and large overlooked in the past, these new results show how, even before a single star explodes as a supernova, massive stars carve out huge bubbles and limit the star formation rates in galaxies.

The findings are being presented by Dr. Elizabeth Harper-Clark and Prof. Norman Murray of the Canadian Institute for Theoretical Astrophysics (CITA) at the 2011 meeting of the Canadian Astronomical Society (CASCA) in London, ON, Canada.

Galaxies are the birthplace of stars. As the stellar population changes, so the galaxy evolves. Yet, the stately pace of this evolution remains unexplained. It is generally believed that the pace of star formation is regulated by the outflow of energy from other stars and possibly black holes.

The lifetime of a Giant Molecular Cloud (GMC, a large star-forming nebula) and the total mass of stars that form within it are crucial to the understanding of star formation rates across a galaxy. In particular, the stars within a GMC can disrupt their host and consequently quench further star formation. Indeed, observations show that our own galaxy, the Milky Way, contains GMCs with extensive expanding bubbles but without supernova remnants, indicating that the GMCs are being disrupted before any supernovae occur.

Radiation from stars interacts with the gas in the surrounding GMC in two main ways: ionization and radiation pressure. Ionization works by forcibly ejecting electrons from atoms at high speed; these electrons then heat up the gas, increasing the gas pressure. Radiation pressure is more subtle and often ignored -- the momentum from the light is transferred to the gas atoms when light is absorbed. These momentum transfers add up, always pushing away from the light source, and produce the most significant effect, according to these simulations.

The simulations performed by Harper-Clark represent the first calculations of the effects of radiation pressure on GMCs and show that this pressure is capable of disrupting such clouds, the main star-forming units in galaxies. "The results suggest that the slow rate of star formation seen in galaxies across the universe may be the result of radiative feedback from massive stars," says Professor Murray, Director of CITA.

Simulating entire GMCs is challenging, due to the large variety of physics that needs to be included and the computational power required to accurately simulate a GMC over tens of millions of years. Using the radiative-magneto-hydrodynamic code Enzo, Harper-Clark ran multiple simulations of GMCs under different conditions.

Harper-Clark robustly found that with only the light emitted by the stars (radiation) during their lifetimes the GMC could be completely blown apart, cutting off star formation after a percentage between 5% and 20% of the original cloud's mass had been converted into stars.

Interestingly, when supernovae were included in the simulations they were found to be unimportant. Both with and without the light from stars, supernovae were not significant on the disruption of the GMC, nor did they alter the subsequent star formation. With no radiation feedback, supernovae exploded in a dense region leading to rapid cooling. This robbed the supernovae of their most effective form of feedback, hot gas pressure. When radiative feedback is included, the supernovae explode into an already evacuated (and leaky) bubble, allowing the hot gas to expand rapidly and leak away without affecting the remaining dense GMC gas. "These simulations suggest that it is the light from stars that carves out nebulae, rather than the explosions at the end of their lives," says Dr. Harper-Clark.

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

User comments

light from massive stars is, by itself, enough to blow apart the nebula

Although this is only "a computer simulation", it may explain how a glowing ball of waste products (photosphere) can accumulate and be suspended above neutron stars to produce ordinary-looking stars like the Sun.

What are galaxies if not a collection of a whole lot of stars? Where does the first stars come from? Are they implying that galaxies appear suddenly in one massive POP, spewing out stars at prodigious rates, before the birth of stars and supernovas can disrupt any further star formation by blowing the gas away? So then they don't really know where stars come from and hence by implication where galaxies come from. This means that the current theories of cosmology and cosmogony are really a lot of hot air as far as explanatory power is concerned. If you cannot explain where stars and galaxies come from or how they are created, you cannot explain anything else. But of course it doesn't mean they should stop trying, just stop pretending they know it all.

@kevinrtrsThe article clearly states that 5% to 20% of the GMC mass is converted into stars before the GMC is crippled by radiation. The remaining gass does not dissappear, some of it may condense into new clouds at later stages unless it is blown entirely out of the galaxy by some extreme star burst formation or perhaps an active galactic nucleus.

Although this is only "a computer simulation", it may explain how a glowing ball of waste products (photosphere) can accumulate and be suspended above neutron stars to produce ordinary-looking stars like the Sun.

Can't happen since there is no neutron star in the Sun. Now the churning idea is reasonable BUT since the heat reaching the surface of the Sun come from reactions that took place a million years ago, according to theory that actually follows known physics, it seems that there might be a bit of lag between the churning and the heat released from the photosphere.

waste products (H/He-rich photosphere

She didn't say that despite you spamming her. She mentioned you but not one word about a neutron star.>>

So where is that minimum? The latest solar minimum did go a couple of years more than normal BUT that just ended and we still don't have new minimum UNLESS there is something causing the temperature to be high anyway. CO2 perhaps?

However a long term minimum should have few if any sunspots for decades and that isn't happening at the moment.>>

We agree that in the first half of the 21st century the solar activity might be lower and even the temperatures might go down.

That doesn't follow from her numbers. Her numbers produce the mid to late 20th century for a new minimum. Funny how that got ignored. Then again the interviewer didn't want to find errors since the site is a denial site.

Its an interesting concept and I suspect it is at least partly true HOWEVER the timing of the minimums have a problem with the present lack of a minimum which should have started 30 or more years ago.

E-mail the story

Disruption of giant molecular clouds by massive star clusters

Note

Your email address is used only to let the recipient know who sent the email. Neither your address nor the recipient's address will be used for any other purpose.
The information you enter will appear in your e-mail message and is not retained by Phys.org in any form.

Your message

Newsletter sign up

Get weekly and/or daily updates delivered to your inbox.
You can unsubscribe at any time and we'll never share your details to third parties.

Your Privacy

This site uses cookies to assist with navigation, analyse your use of our services, and provide content from third parties.
By using our site, you acknowledge that you have read and understand our Privacy Policy
and Terms of Use.